The control over the aggregation of magnetic ions in a non-magnetic semiconductor matrix constitutes a new way to realize semiconductor/ferromagnetic nanocomposites with hitherto unexplored but striking functionalities.  

With this work we show – in the case of the model systems (Ga,Fe)N and Ga,Mn)N fabricated by metalorganic vapor phase epitaxy – that there is a critical and systematic dependence of the crystalline structure, magnetic ions incorporation and macroscopic properties of these composite material systems on the fabrication conditions and on the co-doping with shallow impurities.

For phase-separated (Ga,Fe)N, we show that the controlled formation of various Fe-rich embedded nanocrystals with peculiar stoichiometry and magnetic properties is responsible for the observed contributions to the overall magnetization of the layers, namely: i) paramagnetic – due to dilute Fe3+; ii) ferromagnetic; and iii) a component linear in the magnetic field, associated with antiferromagnetic interactions – originating from  FexN (x ≤ 2) [1]. Furthermore, the effect of Mg co-doping and deposition mode on the Fe distribution is discussed, together with the ways to obtain a controlled and well-defined arrangement of monophase Fe-rich nanocrystals embedded in the GaN host [2].

In the case of (Ga,Mn)N, we demonstrate that co-doping with Mg over a certain threshold of doping allows to modify the charge- and spin-state of Mn via the formation of impurity complexes Mn-kMg, where k depends on the fabrication conditions. The significance of these results is discussed in view of the prospects of embedded magnetic nanocrystals and impurity complexes for photonics and solotronics applications [3].  

[1] A. Navarro-Quezada et al., Phys. Rev. B. 84, 155321 (2010)

[2] A. Navarro-Quezada et al. Appl. Phys. Lett. 101, 081911 (2012)

[3] P. Koenraad and M. Flatté, Nat. Mat. 10, 91-100 (2011)

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